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प्रश्न
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उत्तर
'An electric bulb is rated 250 W-230V'; means that if the bulb is lighted on a 230V supply it consumes 25 ow electrical power or 25 OJ of electrical energy converts into heat and light in 1 second.
The safe Ii m it of current through the bulb is:
I = `"P"/"V" = 250/230` = 1.1 A
Current through a 60W lamp rated for 250V is:
I = `"P"/"V" = 60/250` = 0.24 A
We know that resistance of an appliance remains constant.
Resistance of the 1 amp =
R = `"P"/"I"^2 = 60/(0.24)^2 Omega`
If the line voltage falls to 200 V, power =
P = `"V"^2/"R" = (200 xx 200 xx (0.24)^2)/60` = 38.4 watt
Thus power of the lamp reduces to 38. 4 watt.
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संबंधित प्रश्न
Draw a circuit diagram showing two lamps, one cell and a switch connected in series.
How can you change the brightness of the lamp?
Name two devices which work on the heating effect of electric current.
Find the potential difference required to pass a current of 0.2 A in a wire of resistance 20Ω
Tick(✓) the correct choice in the following:
A three pin plug is connected to the lead for a 1 kW electric iron to be
used on a 250 V supply. Which of the following statements is not correct?
A strong short bar magnet is dropped into a solenoid connected to a
galvanometer as shown in fig. The galvanometer shows a deflection to the left when the current in the coil as seen from above is counter clockwise. Which one of the following shows the correct deflection of the galvanometer when the magnet is at posi tions A, Band C.
Electrical power P is given by the expression P = (Q × V) ÷ time
(a) What do the symbols Q and V represent?
(b) Express the power P in terms of current and resistance explaining the meanings of symbols used there in.
Answer the following question.
An electric lamp of resistance 20 Ω and a conductor of resistance 4 0 are connected to a 6 V battery as shown in the circuit. Calculate: 
(a) the total resistance of the circuit,
(b) the current through the circuit,
(c) the potential difference across the (i) electric lamp and (ii) conductor, and
(d) power of the lamp.
Match the items in column-I to the items in column-II:
| Column - I | Column - II |
| (i) electric current | (a) volt |
| (ii) potential difference | (b) ohm meter |
| (iii) specific resistance | (c) watt |
| (iv) Electrical power | (d) joule |
| (v) electrical energy | (e) ampere |
